Biomedical subjects

M Ramos Silva

Publications and source records attributed to M Ramos Silva.

6 recordsLinked to original sources

PubMed2001

Strong hydrogen-bonded amino acid dimers in L-alanine alaninium nitrate.

The title compound, C3H7NO2*C3H8NO2+*NO3-, contains L-alanine-alaninium dimers bonded via the carboxyl groups by a strong asymmetric hydrogen bond with an O...O distance of 2.4547 (19) A. The neutral alanine molecule exists as a zwitterion, where the carboxyl group is dissociated and the amino group is protonated. The alaninium cation has both groups in their acidic form. The alanine molecule and the alaninium cation differ only slightly in their conformation, having an N-C(alpha)-C=O torsion angle close to -25 degrees. The dimers and the nitrate anion are joined through a three-dimensional hydrogen-bond network, in which the full hydrogen-bonding capabilities of the amino groups of the two alanine moieties are realised.

Alanine↗

PubMed2001

An oxo-centred trinuclear FeIII complex: triaquahexakis(mu2-betaine-O:O')-mu3-oxo-triiron(III) bis(tetrachloromanganate) trichloride hexahydrate.

The title compound, [Fe(3)(C(5)H(11)NO(2))(6)O(H(2)O)(3)](MnCl(4))(2)Cl(3).6H(2)O, contains a triiron core linked by a mu(3)-bridging oxide ion. Each of the iron(III) ions has a distorted octahedral environment, being coordinated, in addition to the oxide ion, by four neutral betaine molecules and one water molecule. The N-alkylated alpha-amino acid betaine is present in the dipolar zwitterionic form and chelates pairs of Fe atoms at the vertices of the triangular [Fe(3)O](7+) ionic core. The Fe complex has a crystallographically imposed D3 symmetry. The water molecules fully exhaust their potential as hydrogen donors, forming a two-dimensional hydrogen-bond network in planes parallel to (001).

Journal Article↗

PubMed2001

Dichlorobis(glycocyamine-O)copper(II).

The title compound, [CuCl2(C3H7N3O2)2], is a new copper(II) complex with glycocyamine [(diaminomethyleneamino)acetic acid], the first complex ever reported with this organic molecule. It is composed of discrete centrosymmetric coordinated CuII monomers, the Cu atoms being located at inversion centers. Each metal ion is square-planar coordinated by two Cl atoms and two glycocyamine O atoms. The coordinating glycocyamine molecule exists as a zwitterion, the H atom from the carboxyl group being transferred to the guanidinium group. A three-dimensional network of hydrogen bonds links the monomers and stabilizes the structure.

Journal Article↗

PubMed2001

Conformational flexibility of tricine as a chelating agent in catena-poly-[[(tricinato)copper(II)]-mu-chloro].

In the polymeric title compound, catena-poly[[(N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycinato-O,N,O')copper(II)]-mu-chloro], [CuCl(C6H12NO5)]n, the Cu2+ ions are chelated by tridentate tricine anions and bridged by chloride ions. The metal ion is five-coordinated, with an approximately square-pyramidal geometry. The [CuCl(C6H12NO5)] units form infinite zigzag chains running parallel to the c axis, with Cu-Cl distances of 2.2209 (14) and 2.7792 (19) A. The tricine anion adopts a conformation intermediate between that found in the crystal structure of the neutral molecule and those reported for the Ni2+ and Zn2+ complexes.

Journal Article↗

PubMed2000

Benzyl 5-carboxy-4-ethyl-3-methylpyrrole-2-carboxylate.

In the title compound, C(16)H(17)NO(4), the benzyloxycarbonyl group is anti to the pyrrolic N atom. The molecules are joined into head-to-head dimers by hydrogen bonds involving the carboxylic acid groups. There is orientational disorder of these groups over two positions with approximately equal occupancy. A weaker hydrogen bond between the pyrrolic N atom and the carbonyl O atom of the benzyloxycarbonyl group joins the dimers into chains running parallel to the [110] direction.

Crystallography, X-Ray↗

PubMed2000

3-Hydroxybenzaldehyde.

The title compound, C(7)H(6)O(2), forms infinite chains where the molecules are hydrogen bonded via the hydroxyl and aldehyde groups, with an O.O distance of 2.719 (3) A. Interchain interactions are weak. The geometry of the ring differs from the ideal form due to the effect of the substituents. Ab initio (Hartree-Fock self-consistent field-molecular orbital and density functional theory) calculations for the free molecule reproduce well the observed small distortions of the ring. In the crystal, the geometry deviates from the ideal C(s) symmetry of the free molecule, as given by the ab initio calculations. The aldehyde and hydroxyl groups are twisted around the single bonds which join them to the ring as a result of the intermolecular hydrogen-bond interactions. These are also responsible for an elongation of the hydroxy C-OH bond compared with that calculated for the free molecule.

Journal Article↗